1. Field of the Invention
The present invention relates to stable graft polymer dispersions of low viscosity and improved dispersibility and polyurethanes prepared therefrom. More particularly, the invention relates to graft polymer dispersions prepared by the improved process employing in situ free radical polymerization of an ethylenically unsaturated monomer or monomers in polyol under such conditions that none of the evaporated monomer is returned to the dispersion, or alternatively, the polymerization proceeds without any reflux of the monomer.
2. Description of the Prior Art
The prior art, as evidenced by U.S. Pat. Nos. 3,652,658; 3,875,258; 3,950,317, and U.S. Pat. Nos. Re. 28,715 and Re. 29,014 teach the preparation of graft polymer dispersions which are useful in the preparation of polyurethanes by the polymerization of ethylenically unsaturated monomers in the presence of polyols. The above patents disclose various methods of preparing graft polyol dispersions. U.S. Pat. No. 3,931,092 teaches the preparation of polymeric solids by polymerizing in the presence of a free-radical initiator and an organic solvent. The solvent concentration employed is from about 1 part to 19 parts by weight per part of the hydroxy-terminated organic compound which has a polymerizable carbon double bond. U.S. Pat. No. 3,953,393 teaches the preparation of graft copolymer dispersions by employing alkylmercaptan chain transferring agents at concentrations from 0.1 to 2 percent by weight based on the weight of vinyl monomer. None of the prior art reveals an awareness of the desirability of conducting the polymerization either without reflux of the monomer or without returning any evaporated monomer to the reaction mixture.